Graphitic steel



Patented Mar. 23, 1948 'niiirto stares Harem ori ice qaaimncernpnFrederickR. Bonte, Canton,

Ohio, assignor to The Timken; Roller Bearing CompanyrGanton; Ohio,acorporation o f Qhio v No'Dravving. Application 'March 23, 1942,

This invention relates to graphitic steels. I

Certain types of graphitic steels are disclosedin Patent No. 2,087,764,granted July 20, 1937,0n-an application filed by me.

improvements in used especially Widely. One of these-generally containsabout 1.5 per cent of carbon and about 1 percent of silicon, While theother is-of similar composition but contains: additionally *a smallamount of molybdenum: I Another type of graphitic steel is disclosed andclaimed in my copending application Serial-No.

347,767, filed July 26,1940, no-w'Patent'No.

2,283,664, dated May 19, 1942.: This latter type,

certain unusual properties; contains invite-preferred embodiment about1.5 percent of-ca-rbon, about 0.4 per cent of manganese, about 0.5 perTwo types of-the steels disclosed and claimed in that patent havebeen vWhich possesses the-properties commonr'to-agraphitic steels but Whichadditionally: possesses cent of molybdenum, about 0.65- per centof-silicon, and about 2.8 per cent of tungsten.-

The graphitic steels described in the foregoing patent and applicationare characterized generally by containing'free graphite and-by theability treatment. They possess high resistance to abrasion, metalpick-up and scoring, andth'ey are classed as being free machining. Suchproperties coupled ,With other desirable physical to develop highhardness upon appropriate heat 5 properties have caused the graphiticste'elstc'i be used extensively for the making of dies of many kinds,punches, spinning, slitting'and forming rolls, breaches, and other toolsused for'related purposes, especially Where resistance/to fatigue andabrasion is requisite.

amounts, but their use siderably.

The graphitic steels made heretofore are hardis being extendedlconenedby quenching into oil, Water or brine," and i none has possessed thecapability of airhardening. The necessity for quenching into a liquid isundesirable in some instances, as in the case of parts ofnon-uniformsection, or partsof relatively great length and smallsection, because "the parts may become distorted as a result ofstrainsset up in the quenching operation. Lik'evvi'se, quenching in liquidcoolant requires" special equipment, and some plants are not suppliedwith be d ficult or undesirable to install: such equipment. v v Maphitic air hardening te l are-avail,

able but many of them must be hardened atvery Not only have those steelsbeen used satisfactorily and in large such equipment, or for variousreasonsit" may fullypresent; Y

b It is among the objects of this invention to pro- 1 Serial No. 435842W4Claims. (01.17542 v must! operate at: temperatures- Whichare relativelyhigh, depending ;-upon--thealloy being cast,

and the operating temperatures may be so high a in some instances thatthe beneficial properties of-the previously used=graphitic steels-arenot vide graphitic'steels and'artieles made therefrom in.Which-"theeproperties generally possessed-by such steels arecombined'with air hardening ability; which are -of relatively simple andinexpensive composition and do not require the use of large amounts ofalloying elements, whichin shapes of relatively great length. orrelatively small. section, Orboth, can behardenedawithout 30f seriousdistortion; and- Which' can be hardenedtto provide.austen-iticstructures; that are adapted for use attemperatures abovethose at which the previously-known .gr-aphitio steels :losehardness eriusly h In accordance with this inventionagraphitic steelnarticles aremade,- from steels containing iromfa'bout 1 to Z-per' centofcarbonabout-c 0-25 to :1;0 percent of chromium, about;0.75zto-1.5 percent ofmanganese about 0.25 to 1.0 .per cent-oi 'molybdenum,' about 1.5to 2.5 percent of nickel,

and about.-0..75 :to" 1.25 percent oisilicon. Within such: ranges itise-preferred for many purposes to form the =xarti'cles from :st'eelscontaining iabout 1.5'per1-ent*bf."carbon,-abouti0.5 per cent-ofchromium;- about- 1.25' per Teen-11* of-manganese,

about"""0.5 "per cent of molybdenum; about 1.75 per cent of nickel,andraboutlzll' percent of silicon Neither the phosphorousvnor the'sulfurcontent should exc'eedabout 05025 per cent.

The-remainder of the steels is iron-together'with impurities in theiamounts customarily encountered m such 'steelsg but it Willibe'understood'that other 'alloying elements may be present providedslowly, to 1380 .the preferred composition .able heat treatment,structure possessing other desirable qualities 75 which reason theremainder of the steels may be said to be effectively iron inasmuch assuch additional alloying elements do not alter the essential characterof products made in accordance with the invention. The foregoingelements are balanced in accordance with customary graphitic steelpractice.

The content of manganese is substantially above that ordinarily used inthe previously known'graphitic steels, and it contributes to the airhardening properties of these steels. Manganese in such amounts andchromium tend to repress graphitization, by forming stable "carbides. Inorder to provide graphitic carbon in the structure, therefore, thesilicon is somewhat higher than in the usual graphitic steels, and Wgraphitization is assisted present. Thus the presence of a functionallyactive amount of graphitic carbon in the structure of the products isassured while producing the other desirable properties that characterizethis invention.

by the nickel which is The steels provided by this invention may be madein accordance with procedures standard in the art for the production ofgraphitic steels. Preferably they are made in an electric furnacefollowing standard killed steel practice, the various alloying elementsbeing introduced suitably in the form of ferro-alloys, or otherwise asdesired.

The ingots are working in a manner treated prior and during hotunderstood in the graphitic steel art, i. e., so that the carbon willremain substantially entirely in the combined form during hot working.Generally speaking, the ingots should be hot Worked, as by rolling o'rforging, at a temperature not over about 1950 F. or 2000 F. to produceshapes of desired form and size for conversion into final products. Incase it is necessary to forge the hot rolled material to form dies orother tools the hot rolled shapes should be heated slowly to 2000 F. andheld until they have been heated through, after which they are forged toshape with care taken that the temperature during forging does not fallbelow about The shaped articles are then graphitized by subjecting themto normalizing and annealing treatments. heating above the criticalrange, suitably at about 1700 F., to cause decomposition and diffusionof carbides. They are then cooled, in accordance with ordinarynormalizing practice, by being removed from the furnace and cooled in'air.

"Thereafter the articles are annealed by reheating them into or abovethe critical range, say by. heating to 1450" F. and holding at thattemperature for four hours. The articles are advantageously at about 20F. per hour, F. where they are held for four hours and then cooled atthe same rate to about 1250 F. Thereafter they are cooled slowly toabout 700 F., after which they are removed from the I'furnace andallowed to air cool; In this manner the carbides are partiallydecomposed with production of:

graphitic carbon and with spheroidization of residual carbides.

Treated in the manner just described, steels of given hereinabove willcontain about 0.5 per cent of free graphite, the remainder of the carbonbeing in combined form. The graphitic carbon confers surface lubricatingqualities desirable in articles provided by the invention, while thecarbides provide, upon suith ehw ar r sistan nd a then cooled To thisend they are normalized by 7 After being graphitized the articles aremachined or otherwise finished to shape and size, after which they aresubjected to a hardening treatment in which they are heated above thecritical range and air cooled. tures can be produced, depending upon theconditions of the hardening treatment.

As indicated above, austenitic structures are produced by hardening heattreatment of articles made in accordance with the invention. For manypurposes it is now preferred to conduct such hardening heat treatment toproduce an austenitic-martensitic structure containing about 10 per centof retained austenite, and it is particularly desirable to use a doublehardening procedure. With sections up to'about 2 inches thick, itsuffices for such purposes usually to pack the articles in a suitablecompound, heat to 1625 F., and cool in air, and then to reharden at1550F. With sections from about 2 inches to 4 inches thick, the firstheating should be about 1650 F., while with sections over 4 inches thefirst hardening should be at about F.; in both cases rehardening iseffected at 1550 F., at which temperature the articles are held untilheated throughout, the exact time depending, of course, upon their mass.On the first hardening there will be. retained a substantial proportionof austenite. The rehardening step is desirable because it givesincreased wearing properties resultant from production of martensite byconversion of some of the austenite. Hardnesses of 60 to 65 R0. areregularly obtainable through'hardening in the manner described. Oneadvantage of these steels is that at higher hardnesses they contain moregraphitic carbonthan the other graphitic steels. Their remarkableproperties are due in part to uniform dispersion of the carbides and thegraphite throughout the structure, both being finely divided.

The austenitic structure which distinguishes these steels from othergraphitic steels has various advantages. Particularly, the products areadequately hard "while being ductile and consequently resistant tofracture. A further consequence is that articles made in accordance withthe invention can be operated at higher tempera-. tures withoutobjectionable loss of hardness, thus Widening substantially the field ofutility of the graphitic steels. As an example, the steels of thisinvention are particularly suited for die casting dies, for which usethe hardness is retained to substantially higher temperatures than inthe previously used non-graphitic steels. It is suitable also for use asdies for hot sizing shell blanks. Articles made as described may beflame hardened to produce true austenitic surfaces which are moreexpensive but have necessarily had to be used heretofore where airhardening ability was necessary.

' As exemplifying the' benefits which fio'w from A variety of structheinvention, a die for drawing switch boxes was made from the preferredembodiment, and it was double hardened as described above. This dieproduced 34,000 pieces before regrinding was necessary. Previously therehad been used regularly for this work a high carbon, high chromium diesteel which cost the user 18 cents per pound more than the steel used inthe practice of this invention, and which presumably Was the bestmaterial that the user had found for this purpose, but the die lifeaveraged only 1000 to 1500 pieces. In consequence of this experience theuser bought a substantial number of dies according to this invention.

A particular advantage is that through the practice of the invention itis possible to efiect hardening without distortion tools ofvariablesection or of considerable length and small section, Whosequenching in oil or water is hazardous. Thus the steels may be heattreated Without distortion and at points where liquid quenchingequipment is lacking.

One of the remarkable properties of these steels is that they arecapable of hardening in oil or water, so that they may be quenched insuch coolants if that is desirable for any reason. It may be noted thatit is rather unusual to find steels which are air hardening and arelikewise capable of oil or water quenching. By quenching in liquid mediathe structures may be varied considerably, and. more so by tempering thequenched articles. Thus they may comprise from to 90 per cent ofaustenite and the balance martensite, or full martensite and othernon-austenitic structures. Hardnesses of 60 to 65 R0. in the hardenedstate can be had thus, and by tempering the hardness is, of course,reduced, e. g. 40 to 50 Re.

The steels likewise possess satisfactory mechanical properties. Forexample, in the annealed state the preferred composition has an ultimatestrength of 135,000 p. s. i., a yield point of 77,500 p. s. i., 17 percent elongation in 2 inches, 34 per cent reduction of area, and aBrinell hardness of 262.

According to the provisions of the patent statutes, I have explained theprinciple and method of practicing my invention and have described whatI now consider to represent its best embodiment. However, I desire tohave it understood that, within the scope of the appended claims, theinvention may be practiced otherwise than as specifically described.

I claim:

1. As a new article of manufacture, a. hot worked and heat treated alloysteel article formed from air hardening steel containing about 1 to 2per cent of carbon, about 0.25 to 1 per cent of chromium, about 0.75 to1.5 per cent of manganese, about 0.25 to 1 per cent of molybdenum, about1.5 to 2.5 per cent of nickel, 0.75 to 1.25 per cent of silicon, and theremainder effectively iron, and characterized by anaustenitic-martensitic structure containing graphitic carbon andspheroidized carbides dispersed finely through the structure, and byhigh resistance to wear.

2. As a new article of manufacture, a hot worked and heat treated alloysteel article formed from air hardening steel containing about 1.5 percent of carbon, about 0.5 per cent of chr0- mium, about 1.25 per cent ofmanganese, about 0.5 per cent of molybdenum, about 1.75 per cent ofnickel, and about 1.0 per cent of silicon, and the remainder effectivelyiron, and characterized by an austenitic-martensitic structurecontaining graphitic carbon and spheroidized carbides dispersed finelythrough the structure, and by high resistance to wear.

3. Alloy steel containin about 1 to 2 per cent of carbon, about 0.25 to1 per cent of chromium, about 0.75 to 1.5 per cent of manganese, about0.25 to 1 per cent of molybdenum, about 1.5 to 2.5 per cent of nickel,about 0.75 to 1.25 per cent of silicon, and the remainder effectivelyiron, and characterized by capability of being hot worked and ofproducing upon heat treatment austeniticmartensitic structurescontaining graphitic carbon and spheroidized carbides dispersed finelythrough the structure.

4. Alloy steel containing about 1.5 per cent of carbon, about 0.5 percent of chromium, about 1.25 per cent of manganese, about 0.5 per centof molybdenum, about 1.75 per cent of nickel, about 1.0 per cent ofsilicon, and the remainder effectively iron, and characterized bycapability of being hot worked and of producing upon heat treatmentaustenitic-martensitic structures containing graphitic carbon andspheroidized carbides dispersed finely through the structure.

FREDERICK R. BONTE.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS OTHER REFERENCES Monypenny: Stainless Iron andSteel, 1931, pp. 139445.

Sherry: Steel Treating Practice, 1929; pp. 133- 135.

American Society for Metals, Metals Handbook, 1939, Pp. 574, 575, 614,and 618.

Symposium on Pearlitic Malleable Cast Iron, published by AmericanSociety for Testing Materials, Philadelphia, Pa., 1936, pages 1, 6, 7,13-16.

Bonte: Graphitic Steels, published in Steel, vol. 109, Nov. 24, 1941,pp. 80, 82, 96 and 100.

